The invention relates to an improved angular rate and acceleration sensor using a force-sensitive resonator.
A number of force-sensitive resonators are described in the prior art. Single vibrating beam force sensors are described in U.S. Pat. Nos. 3,470,400, 3,479,536, 4,445,065, 4,656,383, 4,658,174, 4,658,175, 4,743,790, 4,980,598, 5,109,175, and 5,596,145. Double vibrating beam force sensors referred to as Double-Ended Tuning Forks (DETF) are described in U.S. Pat. Nos. 3,238,789, 4,215,570, 4,372,173, 4,415,827, 4,469,979, 4,531,073, 4,757,228, and 4,912,990. The change in frequency of oscillation of the resonant force sensors is a measure of the applied force.
A number of transducers have been developed which employ force-sensitive resonators to measure pressure, temperature, acceleration, angular rate, and loads.
Pressure transducers and load sensors are described in U.S. Pat. Nos. 4,382,385 and 4,406,966. Load cells and scales employing resonators are described in U.S. Pat. Nos. 4,526,247, 4,751,849, and 4,838,369. A digital temperature sensor is disclosed in U.S. Pat. No. 4,448,546. U.S. Pat. No. 4,510,802 describes a strain sensor with a resonator secured to a support, preferably consisting of a thin plate.
Accelerometers employing resonators are disclosed in U.S. Pat. Nos. 4,091,679, 4,479,385, 4,980,598, 5,109,175, 5,170,665, 5,334,901, and 5,596,145.
Gyroscopic rate sensors that couple to a vibrating resonator are disclosed in U.S. Pat. Nos. 4,510,802, 4,592,223, 4,939,935, 5,456,110, 5,696,323, 5,962,784, and 5,974,879. The development of a mechanical rate sensor in the form of a tuning fork excited by electromagnetism is described by R. E. Barnaby and F. H. Gerring, Aeronaut. Eng. Rev., 12 (1953). A quartz gyroscopic rate sensor with analog output is described by Jan Soderkvist, Sensors and Actuators, A21-A23 (1990). Other rate gyroscopic sensors with analog outputs are disclosed in U.S. Pat. Nos. 4,674,331, 4,930,351, 5,131,273, 5,212,985, and 5,522,249. A silicon mechanization of a dithered structure that couples to discrete acceleration sensors is described in xe2x80x9cAerospace Sensor Systems and Applicationsxe2x80x9d, by Shmuel Merhav, Springer-Verlag (1996). Dithered structures for sensing angular rate are also described in xe2x80x9cModern Inertial Technologyxe2x80x9d by Anthony Lawrence, Springer (1998).
None of the angular rate sensors disclosed in the above-identified patents use force-sensitive resonators or force-sensitive sensors to measure strain-induced forces produced longitudinally in a cantilevered structure and thus do not provide optimum performance.
A digital transducer for providing one or more electrical signals provides a frequency indicative of angular rate of rotation of the transducer about a longitudinal axis and linear acceleration. The transducer includes at least one cantilevered structure having a fixed base, a free end, and a neutral bending plane. A drive mechanism is operatively associated with the cantilevered structure to cause the cantilevered structure to periodically flex back-and-forth along an axis parallel to the neutral bending plane. At least one force-sensitive resonator is integral with or is mounted on the cantilevered structure at a location spaced apart from the neutral bending plane of the cantilevered structure. Bending of the cantilevered structure thus imparts a load to the resonator that changes its resonant frequency. As a result, rotation of the cantilevered structure about the longitudinal axis produces Coriolis acceleration that modulates the resonant frequency of the resonator. The amplitude of the frequency modulation is indicative of the angular rate of rotation. Acceleration applied perpendicular to the neutral bending plane generates force on the resonator whose frequency change is a measure of the applied acceleration.